There are many examples of displays mounted on the head, sunglasses, eyeglasses and the like (for example Perera, U.S. Pat. No. 4,867,551). Perera describes a display mounted on eyeglasses, the limitation of which is the high degree of occlusion of the user's field of view beyond the display, and the use of non-axial optics, which introduces distortion. Other companies, such as VirtualVision, provide displays that are suspended by a cable, gooseneck fixture or other mechanical support in front of one or both of the user's eyes. Similarly, students at the MIT Media Laboratory have been mounting displays from Reflection Technology on eyewear, in order to provide a computer display in a mobile fashion. These approaches also highly limit the user's view of the surroundings.
Generally, head-mounted and helmet-mounted display systems are based on miniature displays having a diagonal dimension of 4 cm or less. The display systems that use such miniature displays must provide a lens near the eye for magnification, and to make possible comfortable viewing at near distances. We term the lens and any other associated optics that must be placed near the eye the “eyepiece.” Most prior art head-mounted systems also place the display (for example a miniature liquid crystal flat panel display) near the eye as well, which requires both a support fixture for the eyepiece, and a conduit for electrical cables to the display. These components (wires, liquid crystal display, illumination source and any other required circuits) are placed within an opaque housing near the eye. Consequently, such systems block a portion of the user's visual field, and also obscure the user's face. For liquid crystal displays, the illumination source accounts for a large amount of the volume of the eyepiece.
In a recent patent (U.S. Pat. No. 6,023,372) we described a method of supporting an eyepiece near the eye at the end of a transparent opto-mechanical structure 10 (FIG. 1). Data or images are relayed to the device by a cable which may comprise wire, one or more optical fibers as described in U.S. Pat. No. 5,715,337, or a fiber optic coherent bundle image conduit. The advantage of this prior art approach is the low obscuration of the user's vision inherent in the use of a transparent opto-mechanical support for the eyepiece. A limitation is the additional weight of the clear optical supporting section.
In U.S. Pat. No. 6,057,966, Carroll describes the use of off-axis projection to an eyepiece (a parabolic mirror) suspended in front of a user's eye on a post. This approach, and others like it, suffers from distortion resulting from the off-axis design.